The present invention relates to the field of computer disk drives, specifically, those having fluid dynamic bearings.
Disk drive memory systems have been used in computers for many years for the storage of digital information. Information is recorded on concentric tracks of a magnetic disk medium, the actual information being stored in the forward magnetic transitions within the medium. The disks themselves are rotatably mounted on a spindle. Information is accessed by a read/write transducer located on a pivoting arm that moves radially over the surface of the rotating disk. The read/write heads or transducers must be accurately aligned with the storage tracks on the disk to ensure proper reading and writing of information.
During operation, the disks are rotated at very high speeds within an enclosed housing using an electric motor generally located inside a hub or below the disks. Such spindle motors may have a spindle mounted by two ball bearing systems to a motor shaft disposed in the center of the hub. The bearing systems are spaced apart, with one located near the top of the spindle and the other spaced a distance away. These bearings allow support of the spindle or hub about the shaft, and allow for a stable rotational relative movement between the shaft and the spindle or hub while maintaining accurate alignment of the spindle and shaft. The bearings themselves are normally lubricated by highly refined grease or oil.
The conventional ball bearing system described above is prone to several shortcomings. First is the problem of vibration generated by the balls rolling on the bearing raceways. This is one of the conditions that generally guarantees physical contact between raceways and balls, in spite of the lubrication provided by the bearing oil or grease. Bearing balls running on the microscopically uneven and rough raceways transmit the vibration induced by the rough surface structure to the rotating disk. Such vibration results in misalignment between the data tracks and the read/write transducer, limiting the data track density and the overall performance of the disk drive system. Further, mechanical bearings are not always scalable to smaller dimensions. This is a significant drawback, since the tendency in the disk drive industry has been to shrink the physical dimensions of the disk drive unit.
As an alternative to conventional ball bearing spindle systems, much effort has been focused on developing a fluid dynamic bearing (FDB). In these types of systems, lubricating fluid, either gas or liquid, functions as the actual bearing surface between a shaft and a sleeve or hub. Liquid lubricants comprising oil, more complex fluids, or other lubricants have been utilized in such fluid dynamic bearings.
The reason for the popularity of the use of such fluids is the elimination of the vibrations caused by mechanical contact in a ball bearing system and the ability to scale the fluid dynamic bearing to smaller and smaller sizes. In designs such as the single plate FDB, two thrust surfaces generally are used to maintain the axial position of the spindle/shaft assembly in relation to other components such as the sleeve.
Clearly, it is essential to maintain the volume, position and integrity of the fluid in a fluid dynamic bearing system. Accordingly, there have been improvements to almost every component of such systems, including the addition of seals, various designs for bearing shapes, specific fluids to be used, and the like.
Thus, there is an interest in the art to assure the volume, position and integrity of fluid in a fluid dynamic bearing system.
The present invention is intended to provide a fluid reservoir to maintain the volume and integrity of the fluid in a fluid dynamic bearing assembly. This and other objectives and advantages are achieved by providing a secondary reservoir in a fluid dynamic bearing design between a bearing and an adjacent component such as a bearing sleeve or seal member.
Specifically, the present invention provides an annular bearing cone for a fluid dynamic bearing in a disk drive comprising: a bottom, a top and a middle; a central annular opening; upper walls angling out from the top to the middle; lower walls angling out from the bottom to the middle to meet the upper walls; and axial grooves in the upper walls of the annular bearing cone. The annular cone may also have at least one recirculation hole in communication with the central annular opening where there are axial grooves on the walls of the central annular opening between the recirculation hole and the top of the bearing cone.